Recently, there have been increasing demands for the silver halide photographic emulsion to have improved photographic properties such as high speed, good graininess, improved sharpness, low fog density and sufficiently high optical image density. These demands are seemingly different from one another, but most of them can be solved by a technique of manufacturing a high-speed and low-fog silver halide emulsion; therefore, it is no exaggeration to say that the technological development of a high-speed and low-fog silver halide emulsion is the largest task imposed on the industry.
Meanwhile, ultra-high speed color photographic light-sensitive materials with ISO speed of more than 1,000 have come to be marketed with the advance in sensitizing technique. This has brought about further problems of increasing fog due to natural radioactive rays (environmental radioactive rays and cosmic rays) and accompanying graininess deterioration, in addition to the conventionally known fogging attributable to heat and moisture in a long-term preservation. The problem is recognized in the industry as an important matter to be solved by all means in order to improve image quality of high-speed light-sensitive materials.
The fog increase and accompanying graininess deterioration caused in a long-term preservation of a high-speed silver halide light sensitive material are reported to be depending upon the amount of silver and gold, or the amount of potassium ions, contained in the light-sensitive material. As preventive measures against such deterioration, there are disclosed a technique to control coating weights of gold and silver per unit area of a light-sensitive material and the weight ratio thereof within specific limits in Japanese Patent O.P.I. Publication Nos. 96642/1989, 96651/1989 and 96652/1989, and as a measure to practice it, a method to remove free gold ions or free gold compounds which are present in places other than the inner portion or surface of silver halide grains. Further, Japanese Patent O.P.I. Publication No. 836/1990 discloses a technique to decrease the amount of potassium ions within a specific limit by replacing them by other ions. However, the amount disclosed in these patents are not necessarily new ones, these amounts are conventionally practiced in the industry; therefore, it is self-explanatory that these techniques are insufficient in solving the above problems. Moreover, those techniques to remove free gold ions or free gold compounds which are disclosed in these patents are considered to be not always advisable in view of the stability and cost in manufacturing. Under the circumstances, more effective measures have been strongly demanded.
The present inventors gave an eye to gold sensitizers, a prime factor of shelf-life deterioration of high-speed light-sensitive materials. In general, there have been used, as gold sensitizers (see U.S. Pat. No. 2,399,083, for example), inorganic gold complex salts such as chloroauric acid, potassium chloroaurate, potassium auriothiocyanate and auric trichloride. However, these salts have a disadvantage of releasing gold ions readily, and as a result a portion of the released gold ions forms a stabilized complex jointly with gelatin and remains in gelatin. Accordingly, deterioration in photographic properties caused by gold sensitizers can be tackled as a problem relating to the chemical properties of these gold sensitizers.